Unmanned aerial vehicle with deployable transmit/receive module apparatus with ramjet

ABSTRACT

A system for bistatic radar target detection employs an unmanned aerial vehicle (UAV) having a ramjet providing supersonic cruise of the UAV. Deployable antenna arms support a passive radar receiver for bistatic reception of reflected radar pulses. The UAV operates with a UAV flight profile in airspace beyond a radar range limit. The deployable antenna arms have a first retracted position for supersonic cruise and are adapted for deployment to a second extended position acting as an airbrake and providing boresight alignment of the radar receiver. A mothership aircraft has a radar transmitter for transmitting radar pulses and operates with an aircraft flight profile outside the radar range limit. A communications data link operably interconnects the UAV and the tactical mothership aircraft, transmitting data produced by the bistatic reception of reflected radar pulses in the UAV radar antenna to the mothership aircraft.

BACKGROUND INFORMATION Field

Embodiments of the disclosure relate generally to bistatic tacticalradar applications employing supersonic unmanned aerial vehicles andmore particularly to a system employing small unmanned air vehicles(UAV) having transmit/receive antennae deployable from a retractedsupersonic cruise position to an extended triangular form.

Background

Aircraft reconnaissance and interdiction has been significantlycomplicated by the appearance of highly accurate and often minimallydetectable antiaircraft systems. Consequently, most current tacticalcombat aircraft entering into contested or hostile airspace are placedat risk. The detection range of these systems may be significant thusrequiring a significant standoff distance to avoid the contestedairspace, often beyond the effective range of radar systems employed incurrent tactical aircraft. The use of stealth aircraft to penetratehostile airspace and accomplish such missions provides a certain levelof increased survivability but such aircraft are highly expensive assetsand are used only upon critical need. Use of UAVs for bistatic radarapplications provides an alternative. However, speed of typical UAVsystem requires significant standoff time for aircraft acting as amothership for deployment.

It is therefore desirable to provide a system with a high speed UAVcomponent for bistatic radar sensing whereby a mothership may remainclear of contested airspace while being able to use radar surveillancefor target identification, acquisition and establishing prosecutabletrackfiles.

SUMMARY

Exemplary embodiments provide a system for bistatic radar targetdetection employing an unmanned aerial vehicle (UAV) having a ramjetproviding supersonic cruise of the UAV. Deployable antenna arms supporta passive radar receiver for bistatic reception of reflected radarpulses. The UAV operates with a UAV flight profile in airspace beyond aradar range limit. The deployable antenna arms have a first retractedposition for supersonic cruise and are adapted for deployment to asecond extended position acting as an airbrake and providing boresightalignment of the radar receiver. A mothership aircraft has a radartransmitter for transmitting radar pulses and operates with an aircraftflight profile outside the radar range limit. A communications data linkoperably interconnects the UAV and the tactical mothership aircraft,transmitting data produced by the bistatic reception of reflected radarpulses in the UAV radar antenna to the mothership aircraft.

The embodiments disclosed provide a method for bistatic radar targetdetection where a UAV is launched and navigated with a ramjet engine atsupersonic cruise to beyond a radar range limit. A mothership aircraftis maintained on a flight profile outside the radar range limit. Antennaarms are extended to act as air brakes reducing speed and providingboresight orientation of Tx/Rx modules for bistatic radio frequency (RF)pulse reception. A high power radar system on the mothership aircraft isemployed to emit radar pulses and receive (Rx) modules on the UAV areemployed as a bistatic receiver to receive reflected radar pulses fromtargets. Target data from the UAV is then transmitted via acommunications data link to the mothership aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawings.

FIG. 1 is a block diagram of the operational elements and deploymentscenario for embodiments as disclosed herein;

FIG. 2A is a top view representation of an embodiment of the UAV withdeployable transmit/receive module apparatus and ramjet with antennae inthe retracted position for cruise;

FIG. 2B is a representation of the embodiment of FIG. 2A with theantennae in the deployed position for skin return reception and airbraking capability;

FIG. 3 is a representation of details of the transmit/receive modulesattachment to the antenna backplane and the antenna deploymentmechanism;

FIG. 4 is a block diagram of system components in the mothershipaircraft and UAV; and,

FIG. 5 is a flow chart of a method for implementing the disclosedembodiments.

DETAILED DESCRIPTION

Current bistatic radar systems employing UAVs provide nose mounted orside mounted antenna with conventional propulsion. This reducesbi-static sensor performance as well as the overall speed of the UAV.The system and methods described herein provide embodiments which solvesthese problems by employing a ramjet in a UAV with deployable sidemounted antennas. The ramjet greatly increases the instantaneousacceleration and top speed of the UAV for ingress into and egress fromthe target area. The front section of the UAV is replaced with a ramjetinlet, instead of the sensor suites. The Transmit/Receive modules (T/RModules) of the Active Electronically Scanned Array (AESA) antenna aremounted on the sides of the UAV in multiple panels. These T/R modulesare installed with forward tilted positions so that when the panelsdeploy the planar face of the T/R modules all face forward directlytowards the direction of motion, reducing the need for beam steering andthus increasing the antenna performance. The deployed antenna panelsalso are employed as air brakes to reduce the velocity of the UAV.Deployment occurs in conjunction of decreasing air intake to the ramjet.In operational concept, when a host aircraft will carry a UAV of thecurrent embodiment and upon a need to increase sensor range on shortnotice, the host aircraft will launch the bi-static UAV with ramjet. TheUAV will transition to the area of interest quickly using ramjet power.Once in the target area, the thrust of the ramjet will be reduced andthe antenna panels will deploy, to collect the radar return from atarget illuminated by radar on the host aircraft. Deployment of theantenna panels will assist in speed reduction of the UAV to maximizesensor collection time.

Referring to the drawings, FIG. 1 shows a mothership aircraft 10 with aradar range limit 12. The radar system of the mothership aircraft 10provides radar pulse power effective to a distance L while detectioncapability of the radar will be nominally L/2. The radar range limit 12is defined as the detection range, L/2. To extend the effective radarrange, a UAV 14 is launched from the mothership aircraft 10. Afterlaunch the UAV 14 is navigated, either autonomously with downloadedmission profile information or directly by aircrew in the mothershipaircraft 10 or a remote land or sea based control station. Transmissions16 from a C2 communication link, to be described in greater detailsubsequently, are employed for communication between the mothershipaircraft 10 and the UAV 14. While in transit between the mothershipaircraft 10 and a target 20 (position 1) a ramjet 18 (to be described ingreater detail with respect to FIG. 2A) is engaged to provide sustainedsupersonic cruise for the UAV 14. The target 20 is beyond the radarrange limit 12 from the mothership aircraft 10. As the UAV 14 travels ona flight profile beyond the radar range limit 12 and approaches thesuspected target 20 (at position 2), antenna arms 22 are deployed (asshown in FIG. 2). Deployment of the antenna arms 22 provides an airbraketo reduce the velocity of the UAV and, as will be described in greaterdetail subsequently, positions transmit (Tx)/Receive (Rx) modules foroptimum geometry with respect to the target 20. While the flight profileof the mothership aircraft 10 remains outside the radar range limit withrespect to the target 20 as shown in FIG. 1, radar illumination of thetarget 20 by the radar in the mothership aircraft, radar pulsesrepresented by arrows 24, creates radar reflections from the targetknown in the art as “skin returns”, as RF pulses represented by arrows26. These skin returns are bistatically received by the Rx modules inthe UAV 14. Sensor data from the Rx modules is transmitted over thecommunication link represented by trace 16′, to the mothership aircraft10 thereby extending the effective detection range of the radar on themothership aircraft. The target 20 may be an air-to-air (A/A) target orand air-to-ground (A/G) target. Upon completion of the desired missionprofile the UAV 14 egresses from the target area (position 3) and may berecovered or destroyed as will be described subsequently. In certainapplications a drone-to-drone communication link, represented by arrow28 may be employed for communications between a second launched UAV 14′and a first launched UAV 14 for navigation information to an identifiedtarget or other tactical information

As shown in FIG. 2A, the UAV 14 incorporates a ramjet 30 having asupersonic inlet with intakes 31. Antenna arms 22 are carried in aretracted position substantially flush with the side profile of the UAV14. As seen in FIG. 2B, upon deployment, the antenna arms 22 are carriedat an extension angle 33 no greater than the tilt angle 32 of the inletintakes 31 to maintain a substantially triangular form for aerodynamicconsiderations in reducing shockwave when transitioning from supersonicto subsonic speed and for maintaining a desired radar cross section(RCS). Deployment of the antenna arms 22 provides aerodynamic braking toslow the UAV 14 to a desired airspeed nominally not less than 0.5 Mach.In an exemplary embodiment the triangular form of the UAV has a noseangle of 60°, substantially identical to the tilt angle 32 providing anextension angle of 30° or less.

Details of the antenna system are shown in FIG. 3. Tx/Rx modules 34 aremounted to the antenna arms 22 with a bias angle 35 complementary toextension angle 33 whereby the boresight 37of the Tx/Rx modules issubstantially aligned with the direction of flight of the UAV 14 forincoming RF pulses 26 from the target. The antenna arms 22 provide abackplane acting as a RF corporate feed (a common feed networkinterconnecting input and output signals of the multiple Tx/Rx modules)to the Tx/Rx modules 34 which may be air or liquid cooled. A deploymentrod 36 pivotally actuates each antenna arm 22 and the deployment rod andantenna arm may both incorporate waveguide or coax for interconnectionto a UAV radar system to be described subsequently and, if the Tx/Rxmodules are liquid cooled, appropriate coolant piping. The Tx/Rx modules34 may be covered with a radome (not shown) for aerodynamic smoothness.The deployment rod 36 may be carried in a pressure cylinder 37 allowingactuation of the deployment rod by pressure feed from a bypass conduit38 from the inlet intake 31. In certain embodiments, the antenna armsmay be deployed at selectable angles other than the extension anglebetween the retracted position and a critical angle position where thedrag caused by the antenna arms reduces the airspeed of the UAV to apoint wherein the UAV is unable to maintain flight above stall speed. Atdeployed positions between the stowed position and a critical angleposition the panels may be used as a brake. Specifically, if the panelsare positioned at a smaller angle, less braking is obtained, at higherangles then more braking will be achieved.

The system components incorporated in the UAV 14 and mothership aircraft10 are shown in FIG. 4. The mothership aircraft 10 incorporates a highpower transmit and receive radar system 40 and a UAV controller 42. Amission management system/pilot vehicle interface system 43, integral tothe mothership aircraft and adapted for interface to a crewmember on themothership aircraft, provides interface control for the radar system 40and the UAV controller 42. The UAV controller may be operated by acrewmember on the mothership aircraft 10 for direct control of the UAVflight profile and UAV radar system. The UAV 14 incorporates a UAVcontrol system 44 which controls the flight profile of the UAV. UAVradar system 46 incorporates the deployable radar antenna arms 22 withthe Tx/Rx modules 34 as described in FIG. 3 as well as a data processingsystem for receiving and processing bistatic radar signals. Typicallythe Tx/Rx modules will operate in receive mode only as Rx modules foracquisition of bistatic signals generated from the mothership aircraftradar. However, in certain applications, the UAV radar system 46 willinclude transmitting capability to supplement the radar transmissionfrom the mothership aircraft 10. A communications data link 48 in themothership aircraft 10 and a mating communications data link 50 in theUAV 14 are operably connected to provide communications between themothership aircraft and the UAV. Data from the communications data link48 to the mission management and pilot vehicle interface system 43represented by arrow 45 provides bistatic radar information from the UAVradar system 46 and data regarding the UAV position and flight profilefrom the UAV control system 44 to the mission management and pilotvehicle interface system 43 for display. Radar commands 47 from themission management and pilot vehicle interface system 43 to the aircraftradar system 40 provide commands to the radar to directionally controlthe radar beam to the intended target. UAV commands 49 from the missionmanagement and pilot vehicle interface system 43 to the UAV controller42 provide input through the communications data link 48 to command theUAV to fly/orbit/loiter in a desired flight profile. In the exemplaryembodiment, an L-band (1 to 2 GHz) data link for line of sightbidirectional communication is employed. The UAV may remain primarily ina receive only mode. The data link will contain messages which will beused to direct and control the UAV's flight control system 44 as well asthe radar system 46, as needed. The UAV will use the data link to reportits location and current air vehicle status back to the host mothershipaircraft as well as transmission of data from the radar system 46. Thecommunications data links 48, 50 may employ data burst or beam agilitycapability for covert operation. The communications data links 48, 50may also employ pre-launch communications elements 52, 54 “hardwire”connected through Ethernet or fiber optic ports 56 for pre-launchcommunication between the mothership aircraft 10 and UAV 14.

In the airspace beyond the radar range limit 12 of the mothershipaircraft 10, UAV 14 provides a passive bistatic receiver for thereflected skin returns 26 from a target 20 by impinging radar pulses 24emitted by the radar of the mothership aircraft 10, which may remain inuncontested airspace. In the exemplary embodiments, the UAV 14 Tx/RXmodules on the antenna arms will operate mothership aircraft 10 whichwill be carrying the transmit/receive radar. The mothership aircraft 10has the capability to carry a radar system with power output of ordersof magnitude of 10 or higher than that of the UAV 14 and thus is itpossible for the mothership aircraft to stay in standoff range andradiate while remaining clear out of harm's way while UAV may need tostay “radio silence” to maintain its low observable nature. Passiveoperation enhances the ability of the location of the UAV 14 to bemasked from hostile radar detection systems. Data characterizingtarget(s) 20 from the bistatically received radar data is thentransmitted by the UAV 14 to the mothership aircraft 10 by datalinktransmission 38.

Accordingly, the UAV is not tethered, but rather the UAV is releasablycoupled to an existing pylon on the mothership aircraft (or othermounting structure) in a manner such that the UAV may be deployed fromand guided by the UAV controller in the mothership aircraft towards atarget beyond the radar range detection limit for the mothershipaircraft, to thereby increase the target detection range such that themothership aircraft can stay out of contested airspace while collectingradar data on a target that would otherwise be out of range.

As described with respect to FIG. 1, the UAV 14 may be retrieved via alow impact landing after a flight profile to a friendly area forrecovery or the UAV will carry a destruct system 58 with explosives forself-destruction purposes on vital communication and radar subsystems inthe UAV. The destruct system 58 may be activated, either as a portion ofthe flight profile or upon loss of data link communications, through theUAV control system 44, or upon instruction from mission management andpilot vehicle interface system 43 through the UAV controller 42 on themothership aircraft 10 transmitted using communications data links 48,50.

As a portion of the UAV control system 44, or connected thereto, anantenna extension system 60 is incorporated to control the extension ofthe antenna arms 22. Upon command by the UAV controller in themothership aircraft through the com link and UAV control system orautonomously by the UAV control system when speed reduction of the UAVfrom supersonic cruise for target acquisition mode, the antennaextension system activates the deployment rods 36 and the antenna armsare extended to the extension angle 33.

The embodiments disclosed herein allow a method of target detection asshown in FIG. 5. A UAV is mounted to a mothership aircraft, step 502,and mission information, potentially including an autonomous flightprofile, may be downloaded from the mothership aircraft to the UAV, step504. The UAV is launched and navigated into contested airspace using theramjet engine for supersonic cruise, step 506, while the mothershipaircraft maintains a flight profile outside a radar range limit inuncontested airspace, step 508. Upon target approach, antenna arms onthe UAV are extended, step 509, to act as air brakes reducing speed andproviding boresight orientation of Tx/Rx modules for bistatic RF pulsereception. The mothership aircraft employs a high power radar system toemit radar pulses, step 510, and the UAV employs the Rx/Tx modules as abistatic receiver to receive reflected radar pulses from targets, step512. The UAV then transmits target data via a communications data linkto the mothership aircraft, step 514. The UAV may additionally receiveflight control information from the mothership aircraft over thecommunications data link, step 516, and may report its location andcurrent status, step 518. Upon completion of the mission profile, theUAV may retract the antenna arms and fly at supersonic cruise employingthe ramjet engine to uncontested airspace and be recovered through asoft landing or other known recovery techniques, step 520.Alternatively, the UAV may self-destruct either autonomously throughcommands from the UAV control system or upon direction from the UAVcontroller on the mothership aircraft, step 522. While described hereinas launched from the mothership aircraft, the UAV may be conventionallylaunched from other ground or airborne assets for the desired flightprofile into contested airspace achieving data link communication withthe mothership aircraft when both have established their respectiveflight profiles.

Having now described various embodiments of the disclosure in detail asrequired by the patent statutes, those skilled in the art will recognizemodifications and substitutions to the specific embodiments disclosedherein. Such modifications are within the scope and intent of thepresent disclosure as defined in the following claims.

What is claimed is:
 1. A system for bistatic radar target detectioncomprising: a mothership aircraft having a radar transmitter fortransmitting radar pulses, said mothership aircraft operating with anaircraft flight profile outside a radar range limit with respect to atarget; an unmanned aerial vehicle (UAV) having a ramjet providingsupersonic cruise of the UAV, and deployable antenna arms supporting apassive radar antenna having a plurality of receive (Rx) modules forbistatic reception of reflected radar pulses, said UAV operating with aUAV flight profile in airspace beyond the radar range limit relative tothe target, said deployable antenna arms having a first retractedposition for supersonic cruise and adapted for deployment to a secondextended position, said second extended position acting as an airbrakeand providing boresight alignment of the Rx modules; and, acommunications data link operably interconnecting the UAV and thetactical mothership aircraft, said communications data link transmittingdata produced by the bistatic reception of reflected radar pulses in theUAV radar antenna to the mothership aircraft.
 2. The system for bistaticradar target detection as defined in claim 1 further comprising a UAVcontroller in the mothership aircraft, said UAV controller operablyconnected to the communications data link and transmitting flightcontrol information to a UAV flight control system to control the UAVflight profile.
 3. The system for bistatic radar target detection asdefined in claim 1 wherein the antenna arms deployed to the secondposition maintain an extension angle not greater than the tilt angle ofan inlet intake of the ramjet engine.
 4. The system for bistatic radartarget detection as defined in claim 1 wherein the passive radarreceiver comprises a plurality of receive (Rx) modules attached to theantenna arms at an angle complimentary to the extension angle.
 5. Thesystem for bistatic radar target detection as defined in claim 3 whereinthe antenna arms in the first retracted position are substantially flushwith a side profile of the UAV.
 6. The system for bistatic radar targetdetection as defined in claim 4 further comprising deployment rodspivotally connected to the antenna arms to deploy the antenna arms 7.The system for bistatic radar target detection as defined in claim 6wherein the deployment rods are carried in a pressure cylinder andactivated by pneumatic pressure from a bypass duct connected to theinlet intake.
 8. The system for bistatic radar target detection asdefined in claim 2 further comprising a self-destruct system in the UAV.9. The system for bistatic radar target detection as defined in claim 6wherein the self-destruct system is operable by the UAV flight controlsystem or the UAV controller.
 10. A method for bistatic radar targetdetection comprising: launching a UAV and navigating the UAV with aramjet engine at supersonic cruise to beyond a radar range limit;maintaining a mothership aircraft on a flight profile outside the radarrange limit; extending antenna arms to act as air brakes reducing speedand providing boresight orientation of Tx/Rx modules for bistatic RFpulse reception; employing a high power radar system on the mothershipaircraft to emit radar pulses; employing receive (Rx) modules on the UAVas a bistatic receiver to receive reflected radar pulses from targets;and, transmitting target data from the UAV via a communications datalink to the mothership aircraft.
 11. The method as defined in claim 10further comprising: mounting the UAV to the mothership aircraft; and,the step of launching the UAV comprises launching the UAV from themothership aircraft.
 12. The method as defined in claim 11 furthercomprising: downloading mission information from the mothership aircraftto the UAV.
 13. The method as defined in claim 12 wherein the missioninformation includes a flight profile for the UAV.
 14. The method asdefined in claim 11 further comprising: receiving flight controlinformation to the UAV from the mothership aircraft over thecommunications data link.
 15. The method as defined in claim 11 furthercomprising: reporting location and current status by the UAV over thecommunications data link.
 16. The method as defined in claim 10 furthercomprising: Retracting the antenna arms and flying the UAV at supersoniccruise to uncontested airspace upon completion of the mission profile;and, recovering the UAV through soft landing or other known recoverytechniques.
 17. The method as defined in claim 10 further comprising:causing the UAV to self-destruct after completion of a mission profile.18. The method as defined in claim 17 wherein the step of causing theUAV to self-destruct is autonomous through commands from the UAV controlsystem.
 19. The method as defined in claim 17 wherein the step ofcausing the UAV to self-destruct occurs upon direction from the UAVcontroller on the mothership aircraft.
 20. An unmanned aerial vehicle(UAV) comprising: a ramjet providing supersonic cruise of the UAV, anddeployable antenna arms supporting a passive radar antenna having aplurality of receiver (Rx) modules for bistatic reception of reflectedradar pulses from a radar transmitter on a mothership aircraft, saidmothership aircraft operating with a flight profile outside a radarrange limit and said UAV operating with a UAV flight profile in airspacebeyond the radar range limit, said deployable antenna arms having afirst retracted position for supersonic cruise and adapted fordeployment to a second extended position, said second extended positionacting as an airbrake and providing boresight alignment of the Rxmodules; and, a communications data link operably interconnecting theUAV and the mothership aircraft, said communications data linktransmitting data produced by the bistatic reception of reflected radarpulses in the UAV radar antenna to the mothership aircraft.